Processes for the hydrocyanation of ethylenically unsaturated organic nitriles to produce the corresponding dinitrile are known. Drinkard et al. U.S. Pat. No.3,496,217 discloses such a process in which the catalyst employed is a zero-valent nickel compound, and the catalyst is promoted by zinc chloride. Downing et al. U.S. Pat. No.3,564,040 discloses a continuous process for the preparation of dinitrile by hydrocyanation using zero-valent nickel catalyst promoted with high amounts of zinc chloride. Rapoport U.S. Pat. No. 4,371,474 discloses a continuous process for carrying out the hydrocyanation reaction using an arylborane as the catalyst promoter.